Signal processing is an important work of load spectrum generation, while wavelet denoise method is regarded as one of the best method in engineering signal processing. So on the purpose of obtaining a good load spectrum of engineering vehicles, db3 wavelet is selected as the mother wavelet. Then the denoise layer number was determined by some comparisons, as well as a proper threshold and threshold function algorithm. Finally a whole process in denoise of the load spectrum of a wheel loader, which is from the selection of the mother wavelet to the determination of the denoise layer number to the selection of the threshold algorithm and the threshold function algorithm, is depicted in this paper. A new coefficient is introduced and a satisfactory result is got. It is safe to conclude that wavelet denoise method is the relative best selection for load spectrum analysis of engineering vehicles.